1. Technical Field of the Invention
The present invention relates generally to transmission systems and, more particularly, to an apparatus, system and method for clip-shaping in such systems.
2. Background of Related Art
Transmission systems using multicarrier modulation are becoming increasingly important. An example of a transmission system using multicarrier modulation is an Asymmetric Digital Subscriber Line (ADSL). Some ADSL modems use DMT, a multi-carrier modulation technique, to achieve high bandwidth efficiency. An ADSL transceiver system generally includes a modem at a central station or office adapted to transmit information in a down-stream signal to a modem at a remote terminal and to receive information in an up-stream signal transmitted by the modem at the remote terminal. Modems generally include a transmitter section and a receiver section isolated by a hybrid. The up-stream and down-stream signals pass through a common transmission medium, typically a twisted-pair telephone line. These type of transmission systems typically have a transmitted signal with a higher peak-to-average ratio (PAR) than single carrier transmission system, and thus generally require components with high precision and high power consumption.
Some current systems attempt to limit PAR levels by hard-clipping the transmitted signal, however, several problems can arise from current clipping techniques. For example, in an effort to reduce a transmitted peak, split peaks can result which subsequently can cause peak growth and/or re-growth near the original peak. Further, as a signal's peak width varies and as peaks occur closely together, PAR reduction becomes more difficult and can lead to bit errors which increases the bit error rate of transmissions.